The present invention relates generally to the field of air control dampers, and more particularly, to those air control dampers which are intended to regulate the volume of air passed along a duct or plenum, or through an opening, and which damper is further adapted to prevent the passage of smoke or fire therethrough when the damper is in a closed position. For discussions of some of the problems encountered in the fire, smoke and air control damper field, please refer to my previously issued U.S. Pat. Nos. 3,381,601; 3,204,548; 3,605,603; and 3,899,156.
In particular, a suitable fire, smoke and air control damper should be easily operable to allow the flow of air therethrough at any of a desired number of predetermined settings between the closed and open positions of the blades with respect to the frame. With respect to the fire and smoke control aspect of such a damper, it is also important that a damper be capable of withstanding intense heat and/or air pressures which impinge on either side of the damper for substantial periods of time during a fire. Due to the extreme conditions to which such a damper is subjected, it is necessary to provide extremely strong blades and a very substantial frame which, together, form a tight, positive seal to effectively shut off the air duct, opening, or plenum. In fact, due to the deficiencies experienced by some practitioners in this field, folding blade fire dampers such as those illustrated in my previously issued U.S. Pat. Nos. 3,866,656; 3,866,657; 3,814,165; 3,401,734; 3,727,663; 3,327,764; and 3,273,632 have been utilized in order to overcome those deficiencies otherwise encountered by some devices utilizing a plurality of rotating blades, each of which blades must form a seal with an adjacent blade as well as the frame, which seal is sometimes prone to leakage in the event that extremely precise alignments and tolerances are not maintained. This problem has been accentuated by the fact that a smoke and fire damper must function effectively years after it is installed in a relatively dirty environment.
Prior art rotating blade fire and smoke dampers have therefore incorporated extremely heavy materials which are not subject to easy bending or deformation in the presence of heat. The blades are mounted by distinct hinge or pivot means which are separately installed for the purpose of aligning each of the blades for rotational movement and to ensure the interengagement of each blade with its adjacent blade to form a seal therebetween which does not open in the presence of heat or excessive pressures, such as those which might be encountered during a fire.